Downhole uses of piezoelectric motors

ABSTRACT

A sampling system used in collecting samples of connate fluid from within hydrocarbon bearing formations. The sampling system comprises a sonde disposed within a wellbore formed proximate to the formation of interest. The sonde includes a sample probe insertable into the formation and a drawdown pump in fluid communication with the sample probe. The drawdown pump is motivated by an associated electrically responsive material, where the electrically responsive material can be comprised of a piezoelectric material, a electroactive polymer, or some other electrically responsive material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of hydrocarbon production.More specifically, the present invention relates to an apparatus forsampling connate fluid of a hydrocarbon bearing formation.

2. Description of Related Art

The sampling of connate fluid contained in subterranean formationsprovides a method of testing formation zones of possible interest withregard to hydrocarbon bearing potential. This method involves recoveringa sample of any formation fluids present for later analysis in alaboratory environment while causing a minimum of damage to the testedformations. The formation sample is essentially a point test of thepossible productivity of subsurface earth formations. Additionally, acontinuous record of the control and sequence of events during the testis made at the surface. From this record, valuable formation pressureand permeability data as well as data determinative of fluidcompressibility, density and relative viscosity can be obtained forformation reservoir analysis.

Generally connate fluid sampling involves disposing a sonde 10 into awellbore 5 via a wireline 8. Oppositely located on the outer portion ofthe sonde 10 usually are a sample port 14 and an urging means 12. Whenthe sample port 14 is proximate to a formation of interest 6, the urgingmeans 12 is extended against the inner surface of the wellbore 5 therebyengaging the sample port 14 into the formation 6. The engagement of thesample port 14 pierces the outer diameter of the wellbore 5 and enablesfluid communication between the connate fluid in the formation 6 and thesample port 14. As will be described in more detail below, after pushingthe sample port 14 into the formation 6, the connate fluid can besiphoned into the sonde 10 with a pumping means disposed therein.

Early formation fluid sampling instruments, such as the one described inU.S. Pat. No. 2,674,313, were not fully successful as a commercialservice because they were limited to a single test on each trip into theborehole. Later instruments were suitable for multiple testing; however,the success of these testers depended to some extent on thecharacteristics of the particular formations to be tested. For example,where earth formations were unconsolidated, a different samplingapparatus was required than in the case of consolidated formations.

Down-hole multi-tester instruments have been developed with extendablesampling probes that engage the borehole wall and withdraw fluid samplesfrom a formation of interest as well as measure pressure of the fluidwithin the formation. Traditionally these downhole instruments comprisean internal draw-down piston that is reciprocated hydraulically orelectrically for drawing connate fluid from the formation to theinstrument.

Generally, the down-hole multi-test sampling devices incorporate a fluidcircuit for the sampling system which requires the connate fluidextracted from the formation, together with any foreign matter such asfine sand, rocks, mud-cake, etc. encountered by the sampling probe, tobe drawn into a relatively small volume chamber and which is dischargedinto the borehole when the tool is closed. An example of such a devicecan be found in U.S. Pat. No. 4,416,152. Before closing, a sample can beallowed to flow into a sample tank through a separate but parallelcircuit. Other methods provide for the sample to be collected throughthe same fluid circuit.

Another example of a circuit used in the sampling of connate fluid isshown in FIG. 2. Here connate fluid is motivated from the formation 6via the sample port 14 and a sampling circuit 22 with a pump 20.Reciprocating action of a piston 19 within the pump 20 causes pressuredifferentials that draw the connate fluid into the pump 20. Theactuation means for the pump 20 is, produced by a pressure source 26 anddelivered to the pump 20 by a hydraulic circuit 24. Check valves 28strategically located within the hydraulic circuit 24 and the samplingcircuit 22 direct the fluid flow within these circuits. A more detaileddescription of this circuit can be found in Michaels et al., U.S. Pat.No. 5,303,775.

Mud filtrate is forced into the formation during the drilling process.This filtrate must be flushed out of the formation before a true,uncontaminated sample of the connate fluid can be collected. Often thisfiltrate becomes lodged within the sample port 14 and hinders connatefluid flow to the sampling device. Prior art sampling devices have afirst sample tank to collect filtrate and a second to collect connatefluid. The problem with this procedure is that the volume of filtrate tobe removed is not known. For this reason it is desirable to pumpformation fluid that is contaminated with filtrate from the formationuntil uncontaminated connate fluid can be identified and produced.Conventional down-hole testing instruments do not have an unlimitedfluid pumping capability and therefore cannot ensure complete flushingof the filtrate; contaminant prior to sampling.

Estimates of formation permeability are routinely made from the pressurechange produced with one or more draw-down piston. These analysesrequire that the viscosity of the fluid flowing during pumping be known.This can be achieved by injecting a fluid of known viscosity from thetool into the formation and comparing its viscosity with recoveredformation fluid. The permeability determined in this manner can then bereliably compared to the formations in off-site wells to optimizerecovery of fluid.

When exposed to an open hole, the fluid characteristics of formationfluid can change rapidly, thus it is important that the formation fluidbe removed as quickly as possible. However, it is important that theformation flow rate be regulated in order to prevent dropping the fluidpressure below its “bubble-point” since measuring separated fluids doesnot result in a representative sample. After having these componentscome out of solution, they typically cannot be recombined which resultsin an unrepresentative sample having altered fluid properties.

Recently developed reservoir testing devices are capable of measuringthe bubble-point pressures of the connate fluid at the time of samplecollection. This can be accomplished using known techniques of lighttransmissibility to detect bubbles in the liquid. However this methodhas some drawbacks when particulate matter is present in the fluidthereby resulting in sometimes erroneous results. Other methods includetrapping a known volume of formation fluid and increasing its volumegradually at a constant temperature. The measured changes in volume andpressure provide a plot of pressure vs. volume in order to ascertain thevalue of the bubble-point. This value is estimated within the region ofthe plot where the pressure and volume graph is no longer linear.

Unfortunately the pumping devices currently in use with the samplingdevices have inherent drawbacks. For example, control of the electricalor hydraulic actuation means of the presently used pumping systems isnot accurate that in turn results in an inability to fully control thespeed of the pumps. Not being able to fully control pump speed prohibitsthe capability of ceasing pumping operations should the pressure of theconnate fluid fall below its bubble point and also hinders the abilityto accurately measure the bubble point. Since sampling connate fluid atpressures below its bubble point negatively affects the accuracy of thesampling data results. Therefore a need exists for a means of samplingconnate fluid whereby the connate fluid can be obtained and analyzed atknown pressures without altering the state of the sample.

BRIEF SUMMARY OF THE INVENTION

The device of the present disclosure includes a formation fluid testingdrawdown pump comprising a piston, a cylinder formed to receive thepiston therein, and a motive device operatively coupled to the piston.The motive device is comprised of material responsive to electricalstimuli. Alternatively the material responsive to electrical stimuli canbe a piezoelectric composition or a electroactive polymer. Optionallythe piezoelectric composition may be a single piezoelectric segment orat least two distinct piezoelectric segments. The motive device of thedrawdown pump can optionally be a piezoelectric motor, where thepiezoelectric motor is selected from the group comprising a linearpiezoelectric motor and a rotary piezoelectric motor. The operativecoupling of the drawdown pump may be comprised of a direct mechanicalattachment between said motive device and said piston as well as ahydraulic circuit.

The formation testing drawdown pump may further comprise a feed backloop and a pump control, where the feed back loop comprises a pressuremonitoring device in operative cooperation with the pump control. Thepressure monitoring device provides data representative of fluidpressure within the cylinder and wherein the pump control isprogrammable for controlling the operation of said drawdown pump inresponse to the data representative of fluid pressure within thecylinder to ensure the fluid pressure within the cylinder remains aboveits bubble-point pressure.

A method of sampling connate fluid from within a subterranean formationis disclosed herein comprising inserting a drawdown pump within awellbore adjacent the subterranean formation, providing a fluidcommunicative path between the drawdown pump and the subterraneanformation, and operating the drawdown pump with a motive device. Themotive device of the present method is operatively coupled to thedrawdown pump and comprises material responsive to electrical stimuli.The method further comprises providing electrical energy to the motivedevice. The material of the present method may be comprised of apiezoelectric composition that is a single segment or at least twodistinct segments. The piezoelectric composition of the present methodmay comprise a piezoelectric motor, where the piezoelectric motor isselected from the group comprising a linear piezoelectric motor and arotary piezoelectric motor. Optionally, the material responsive toelectrical stimuli of the present method may be comprised of anelectroactive polymer.

The operative coupling of the present method may be comprised of adirect mechanical attachment between the motive device and the pistonand may also include a hydraulic circuit. The method may furthercomprise monitoring the pressure within the cylinder. The present methodmay further comprise controlling operation of the drawdown pump based onthe monitored pressure within the cylinder thereby ensuring the pressurewithin the cylinder remains above the bubble-point pressure of thesampled fluid. The drawdown pump may operate under constant pressure orunder constant volumetric flow.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING.

FIG. 1 depicts in a partial cutaway side view of a sampling sondedisposed in a wellbore.

FIG. 2 illustrates a prior art drawdown pump.

FIGS. 3A-3D portray electrically responsive materials in a perspectiveview.

FIG. 4 shows a cutaway view of one embodiment of a drawdown pump inaccordance with the disclosure herein.

FIG. 5 illustrates an embodiment of a drawdown pump in accordance withthe disclosure herein.

FIG. 6 depicts a partial cutaway view of an embodiment of a drawdownpump in accordance with the disclosure herein.

DETAILED DESCRIPTION OF THE INVENTION

With reference now to the drawings herein, one embodiment of a drawdownpump 56 in accordance with the present invention is illustrated in acutaway view in FIG. 4. In this embodiment the drawdown pump 56comprises a housing 57 that encompasses a cylinder 58 on one end andhaving a cavity 66 on its other end. The cylinder 58 should besubstantially cylindrical and formed to receive a piston 68 within. Thepiston 68, having a disklike configuration, should likewise have anouter diameter that is substantially circular and formed forreciprocating axial travel within the cylinder 58. The cavity 66, whileshown as substantially cylindrical, can have other shapes and can alsohave a varying cross sectional area along its length. As will bedescribed in more detail later, the cavity 66 should be formed toreceive a section of electrically responsive material.

A seal 69 can be provided on the outermost circumference of the piston68. The seal 69 should preferably be comprised of a resilient pliablematerial, such as a polymer, that is capable of providing a pressureseal across the outer diameter of the piston 68. This pressure sealshould thereby isolate the pressure within the cylinder 58 on the sideof the piston face 71 from the cylinder pressure along the piston rod70.

The drawdown pump 56 of FIG. 4 further comprises a fluid inlet line 60that terminates on one of its ends at an inlet port 61 formed in thepump housing 57. Since the inlet port 61 traverses the through theoutside of the housing 57 and into the cylinder 58, the fluid inlet line60 is therefore in fluid communication with the cylinder 58. The otherend of the fluid inlet line 60 is in fluid communication with a sampleprobe 14. An inlet check valve 62 is included with the fluid inlet line60. Fluid can flow across the inlet check valve 62 only in the directiontowards the inlet port 61 but is prevented from flowing across the inletcheck valve 62 from the inlet check valve 62 towards the sample probe14.

This embodiment of the drawdown pump 56 further includes a fluid exitline 64 connected on one of its ends at an outlet port 65 and in fluidcommunication on its other end with a fluid storage tank (not shown). Anoutlet check valve 63 resides on the fluid exit line 64 whoseorientation allows fluid flow from the drawdown pump 56 to fluidstorage, but prevents flow from the fluid storage tank to the drawdownpump 56. Like the inlet port 61, the outlet port 65 is formed throughthe outer surface of the housing 57 thereby allowing fluid communicationbetween the fluid exit line 64 and the cylinder 58.

With reference now to FIGS. 3A-3D, examples of electrically responsivematerial (ERM) are shown in a perspective view. Electrically responsivematerial converts electrical energy into mechanical energy and canexpand or contract when exposed to electrical stimuli. The electricallyresponsive material can include piezoelectric composites, electroactivepolymers, artificial muscles and the like.

When a voltage is applied to the piezoelectric material, the materialwill experience a strain that causes it to expand. When the voltage isremoved, the strain is removed and the material contracts. Anon-limiting list of potential piezoelectric materials for use withembodiments of the present invention includes ceramics, quartz,poly-crystalline piezoelectric ceramics, and quartz analogue crystalslike berlinite (AlPO4) and gallium orthophosphate (GaPO4), ceramics withperovskite or tungsten-bronze structures (BaTiO3, KNbO3, LiNbO3, LiTaO3,BiFeO3, NaxWO3, Ba2NaNb5O5, Pb2KNb5O15).

Suitable electroactive polymer materials include any substantiallyinsulating polymer or rubber (or combination thereof) that deforms inresponse to an electrostatic force or whose deformation results in achange in electric field. More specifically, exemplary materials includesilicone elastomers, acrylic elastomers such as VHB 4910 acrylicelastomer, polyurethanes, thermoplastic elastomers, copolymerscomprising PVDF, pressure-sensitive adhesives, fluoroelastomers,polymers comprising silicone and acrylic moieties, and the like.Polymers comprising silicone and acrylic moieties may include copolymerscomprising silicone and acrylic moieties, polymer blends comprising asilicone elastomer and an acrylic elastomer, for example.

With regard to the electrically responsive material of the embodiment ofFIGS. 3A-3D and FIG. 4, the electrically responsive material expandswith the application of an electrical stimulus. This expansion isillustrated with reference to a comparison of FIGS. 3A and 3B. Anexample of an ERM 50 of length L₁ is shown in FIG. 3A in its relaxed orunresponsive state. Illustrating the expansive nature of electricallyresponsive material, FIG. 3B depicts an ERM 50 a illustrating how thematerial responds to an applied electrical stimuli. In FIG. 3B, the ERM50 a has expanded over that of the ERM 50 of FIG. 3A and its length hasincreased from L₁ to L₁+ΔL₁; where L₁+ΔL₁ is greater than L₁. Theincrease is a function of the dimensions of the un-stimulated materialas well as the amount of current or voltage applied to the material. Itis believed that it is well within the capabilities of those skilled inthe art to determine appropriate dimensions and applied electrical powerin order to attain the desired means and ends of the present invention.

Alternatively, with reference now to FIGS. 3C and 3D, the electricallyresponsive material can be a segmented ERM 52 comprised of at least twosegments 54 sequentially stacked in an axial configuration. FIG. 3Cdepicts in perspective view a segmented ERM 52 in a relaxed state, uponapplication of applied electrical energy to the segmented ERM 52 itexpands to an expanded ERM 52 a (FIG. 3D) from a length L₂ to a lengthL₂+ΔL₂, where L₂+ΔL₂ is greater than L₂. An advantage of greater controland flexibility of ERM expansion can be realized by the segmentedembodiment. Here a single segment 54 can be expanded by selectivelyapplying electrical energy, or the collective segments 54 can besequentially expanded to affect a manner of the expansive stroke appliedby expansion of the segmented ERM 52. It should be pointed out thatwhile linear expansion is illustrated in FIGS. 3A-3D, the ERMs (50, 52)can expand in a radial fashion as well.

In operation, connate fluid resident within the formation of interest 6enters the sample probe 14, travels through the fluid inlet line 60 andinto inlet port 61, thereby filling the cylinder 58. Generally when thecylinder 58 is being filled with connate fluid the piston 68 is in thedownstroke mode and moving towards the cavity 66. This movement of thepiston 68 can be produced by the pressure differential across the piston68 caused by the presence of the fluid, or by a spring (not shown)disposed within the cylinder 58 driving the piston backwards.

When a desired amount of fluid fills the cylinder 58, an electricalstimulus is applied to the ERM 50 disposed within the cavity 66. Itshould be pointed out that the segmented ERM 52 can be used in lieu ofthe ERM 50, or these varying embodiments can be used concurrently. Aspreviously discussed, the electrical stimulus causes the ERM 50 toexpand; this expansion in turn pushes against the piston rod 70 andurges it out of the cavity 66. As the piston rod 70 is moved out of thecavity 66 (the upstroke mode) the piston 68 travels across the cylinder58 thereby imparting a motivating force onto the fluid within thecylinder 58. This motivating force pressurizes the fluid thereby causingit to move from the cylinder 58 through the outlet port 65 onto thefluid storage tank via the fluid exit line 64. As is well known, thestrategic positioning and orientation of the inlet and outlet checkvalves (62, 63) allows fluid flow into the cylinder 58 from theformation 6 during the downstroke mode and from the cylinder 58 to fluidstorage during the upstroke mode.

Optionally, as shown in dashed lines in FIG. 4, the connate fluid inletline 60 a connects to the housing 57 at the inlet port 61a. Here theinlet port 61 a pierces the connate pump 56 in an area of the housing 57proximate to the ERM cavity 66. In this configuration urging the piston68 into the cylinder 58 by expansion of the ERM 50 reduces the pressureon the backside of the piston 68 thus drawing fluid in from theformation 6. Furthermore, like the inlet port 61 a, the outlet port 65 aof this alternative embodiment is similarly positioned proximate to theERM cavity 66. Thus the fluid drawn into the cylinder 58 duringexpansion of the ERM 50 is urged out of the cylinder 58 on thedownstroke of the piston 68.

The embodiment of the drawdown pump 56a shown in FIG. 5 comprises anelongated housing 57 a having a substantially cylindrical cylinder 58 aformed to receive a piston 68 a axially therein. Like the piston 68 ofthe embodiment of FIG. 4, the piston 69 a has a disk-like configurationsuitable for axial travel within the cylinder 58 a. However theassociated piston rods (74, 75) of this embodiment extend respectivelyfrom both the first and the second piston face (71 a, 72 a). The pistonrods (74, 75) extend into corresponding forward and rearward cavities(76, 73) disposed at the opposite ends of the cylinder 58 a. Further, inthis embodiment, fluid inlet lines 60 a connect to the cylinder 58 a viainlet ports 61 a on both sides of the piston 68 a. Similarly, fluidoutlet lines connect to the cylinder 58 a via outlet ports 65 a that arealso situated on both sides of the piston 68 a. The inlet lines 60 a arein fluid communication on their other end with the sample probe therebyenabling connate fluid to flow into the cylinder 58 a through theselines. As in the case of the embodiment of FIG. 5, in this embodimentthe other end of the fluid exit lines 64 a connects to a fluid sampletank. Inlet check valves 62 a are included within the inlet line 60 athat limit fluid flow direction only to the cylinder 58 a. Outlet checkvalves 63 a are also provided with the exit lines 64 a that allow fluidflow from the cylinder to the fluid sample tank but prevents flowreverse directional flow. A quantity of ERM 50 is included within eachcavity (76, 73).

In the operation of the embodiment of FIG. 5 axial movement of thepiston 68 a is effectuated by stimulating one of either ERM 51 withinthe forward cavity 76, or ERM 53 within the rearward cavity 73. As notedabove, stimulation of any electrically responsive material can cause itto expand. In the case of the drawdown pump 56 a, expansion of eitherERM 51 or ERM 53 urges the piston 68 a along the axis of the cylinder 58a. Movement of the piston 68 a in either direction increases the fluidpressure within the cylinder 58 a in the portion that the piston 68 a ismoving towards, thus urging any fluid within that portion to the fluidstorage tank via the corresponding fluid exit line 64 a. Moreover, inthe other portion of the cylinder 58 a, the fluid pressure isdecreasing, thus drawing the connate fluid out of the formation 6, intothe sample port 14, and into that portion of the cylinder 58 a. When thepiston 68 a reaches the end of its stroke, the electrical powerstimulating the expanded ERM (51 or 53) is terminated and electricalpower is then applied to the other ERM (51 or 53) to repeat the processof simultaneously urging fluid from one portion of the cylinder 58 a anddrawing fluid into the other portion. Accordingly, the electricalstimulus should not be applied to both ERM 51 and ERM 53 simultaneously,but instead should be applied in discrete sequences. Use of the presentinvention thereby enables samples of connate fluid to be drawn, atpressure, from a formation of interest 6 and stored within a storagetank for later analysis. Sustaining the connate fluid at pressuremaintains the sample above its bubble point thereby preserving all theconstituents within the sample.

The embodiment of the drawdown pump 78 of FIG. 6 comprises a piston 80,a cylinder 82, a piston rod 86, an ERM segment 88, an anchor rod 92, abase 94, an expansion stroke pinch brake 100, a compression stroke pinchbrake 102, and an optional dashpot 98. The base 94 further includes legs95 that extend perpendicularly away from the main body of the base 94.The legs 95 contain a first aperture 97 and a second aperture 99 inwhich the pinch brakes (100, 102) are respectively disposed. Thecylinder 82 is elongated and is formed within a generally cylindricalcylinder housing 84. The inner diameter of the cylinder 82 is formed toaxially receive the piston 80 therein and allow for axial reciprocationof the piston 80. The piston 80 has a disklike configuration with acircular outer diameter that should match the dimensions andconfiguration of the inner diameter of the cylinder 80. Preferably therespective dimensions of the outer circumference of the piston 80 andthe inner diameter of the cylinder 82 are sufficiently close to create apressure seal along the outer diameter of the piston 80. Seals (notshown) may be disposed on the outer diameter of the piston 80 forproviding the pressure seal.

The piston rod 86 is attached to the rearward side of piston 80 andextends outside of the cylinder housing 84 through an opening 85 formedon the rear face of the housing 84. The piston rod 86 is connected tothe forward side of the ERM 88 on its other end. An annular seal 96 canbe included around the piston rod 86 within the cylinder 82 and adjacentthe opening 85 for preventing fluid flow through the opening 85.

Between the cylinder housing 84 and the ERM 88, the piston rod 86 passesthrough the expansion stroke pinch brake 100. The expansion stroke pinchbrake 100 fits within a first aperture 97 formed through one of the legs95. The inner diameter of the first aperture 97 is greater than theouter diameter of the piston rod 86 thus providing a space for the pinchbrake 100 to reside therein. As shown, the pinch brake 100 is a singleannularly shaped element circumscribing a portion of the length of thepiston rod 86; but the pinch brake 100 can also be comprised of one ormore elements radially disposed within the space between the piston rod86 and the diameter of the first aperture 97.

Selective activation of the pinch brake 100 impinges the brake 100 uponthe piston rod 86 with sufficient force to effectively bind the pistonrod 86 to the leg 95 thereby preventing movement of the piston rod 86with respect to the leg 95. Examples of suitable material for the brakeinclude an inflatable packer, extending members, and electricallyresponsive materials, such as piezoelectric material and electroactivepolymers.

The anchor rod 92 is connected to the rearward side of the ERM 88 on oneend and passes through the compression stroke pinch brake 102 beforeterminating within the optional dashpot 98. Optionally, the other end ofthe anchor rod 92 is inserted into the dashpot 98 via an opening 93formed through the wall of the dashpot 98. The dashpot 98 should containa compressible fluid, such as for example but not limited to siliconeoil, brine, or formation fluid. Seals 96 are provided adjacent theopening 93 for retaining the fluid within the dashpot 98.

The ERM segment 88 is preferably comprised of an electrically responsivematerial such as a piezoelectric composite, an electroactive polymer, orany other substance responsive to external electrical stimuli. The ERMsegment 88 of the embodiment of FIG. 6 is shown as a series of stackedelements 90, where each element has substantially the same dimensions.However, the ERM segment 88 can alternatively be comprised of a singlenon-segmented portion of electrically responsive material. Further, thestacked elements 90 can also be of varying dimensions. Additionally, thespecific material of the individual elements 90 can vary, for example,one or more of the elements 90 might be comprised of a piezoelectricmaterial while the remaining elements 90 may be comprised of anelectroactive polymer.

In operation, the embodiment of the drawdown pump 78 of FIG. 6 operatesin a similar fashion to the above described drawdown pumps (56, 56 a),that is the drawdown pump 78 is in fluid communication with the sampleprobe 14 via a conduit 15. Connate fluid is drawn into the cylinder 82by the pressure differential that exists between the cylinder 82 and theformation 6. The differential pressure can be created by lowering thepressure within the cylinder by urging the piston 80 axially rearwardthrough the cylinder housing 84. Movement of the piston 80 isaccomplished by selectively activating the ERM segment 88 in combinationwith both the expansion stroke pinch brake 100 and the compressionstroke pinch brake 102. For example, stimulating the ERM segment 88while simultaneously releasing the compression stroke pinch brake 102allows the ERM segment 88 to expand in response to the applied externalelectrical stimulus. Expansion of the ERM segment 88 thereby slides theanchor rod 92 through the compression stroke pinch brake 102 in adirection away from the ERM segment 88. Upon completion of the expansionstroke of the ERM segment 88 the compression stroke pinch brake 102 isactivated thereby clamping the anchor rod 92 therein. Then the externalstimulus is removed from the ERM segment 88 while the expansion strokepinch brake 100 is in the release mode. Removing the electrical stimulusfrom the ERM segment 88 allows the ERM segment 88 to contract in size toits normal or relaxed state. Contraction of the ERM 88 in combinationwith the release of the expansion stroke pinch brake 100 pulls thepiston rod 86 in the direction of the ERM segment 88 thereby urging thepiston 80 through the cylinder 82 in a rearward direction.

The piston stroke length realized during each sequence ofrelease/activation steps is dependent upon the amount and type of theelectrically responsive material of the ERM segment 88 as well as theamount and type of external stimulus applied. Consecutively repeatingthe above described release/activation and stimulus steps produces an“inch-worm” effect on the piston travel enabling the drawdown pump 78 todraw in a suitable amount of connate fluid within the cylinder 82 forsubsequent analysis. Typical fluid sampling volumes can range from about30 cc to in excess of 900 cc, and often in the range of about 56 cc.However the actual amount of fluid sampled is dependent on theparticular formation from which the fluid is being drawn, thus thevolume of the cylinder 82 should be able to accommodate the amount offluid to be sampled.

Due to the highly responsive qualities of electrically responsivematerials, the speed and stroke of the piston 80 can be tightlycontrolled to ensure that the pressure within the cylinder 82 remainsabove the bubble point pressure of the connate fluid. Accordingly one ofthe many advantages realized by the drawdown pump of the presentdisclosure is that the measured discrete movements of the piston 80 doesnot produce the large dynamic forces caused by theacceleration/deceleration of typical currently used drawdown pumpmotors. Furthermore, due to the highly responsive nature of electricallyresponsive material, the speed of operational cycles of drawdown pumpsof the present disclosure is well within acceptable limits ofoperational usage.

The pressure within the cylinder 82 may be monitored with the attachedpressure monitoring device 83. Implementation of the pressure monitoringdevice 83 also provides the ability to control the actuation of thedrawdown pump 78 to ensure the pressure within the cylinder 82 remainsabove the bubble point of the sampled fluid therein. The drawdownsequence can occur under constant pressure or under constant volumetricflow rate. The pressure measured by the pressure monitoring device 83 isconveyed via a feed back loop 87 to the pump control 79. The pressuremonitoring device 83 can be a pressure gauge, and can detect thepressure in any currently known or later developed means of pressuremonitoring. For example, the pressure monitoring device 83 can monitorpressure pneumatically or with transducers that convert mechanicalenergy to electrical, such as a quartz element or piezoelectriccomponent. The measured pressure can be measured and obtained in digitalor analog form.

The pump control 79, as is known in the art, may be comprised of aprogrammable circuit, such as a computer or microprocessor, having beenprogrammed to analyze the value of the measured pressure within thecylinder 82 and compare it to the connate fluid bubble point pressure.Should these two pressures both reside within a predetermined pressurerange, the pressure control 79 may be programmed to adjust the operationof the drawdown pump 78 to ensure the pressure of the fluid in thecylinder 82 remains above its bubble point pressure. The data commandsare preferably in digital form and are transferred to the operationalcomponents 77 of the drawdown pump 78 via the control loop 81. Theoperation components 77 include the items enclosed by the dashed line ofFIG. 6, as well as the components used to supply and control theelectrical signal(s) applied to the items within the dashed line. Thoseskilled in the art are capable of establishing a proper pressure rangeabove that which the cylinder pressure should remain. It is also withinthe capabilities of those skilled in the art to program a control systemfor comparing measured pressures with bubble point pressures andaffecting pump controls when these pressures fall within the specifiedrange.

Furthermore, an additional advantage realized by the responsive materialof the ERM segment 88 is that the discrete inch-worm movements of thedrawdown pump 78 simulate a continuous or analog movement of the piston80 that minimizes or eliminates the dynamic pumping effects experiencedby current drawdown pumps. When it is desired to empty the cylinder 82of fluid, the release/activation sequence may be reversed to urge thepiston 80 into the cylinder 82 and thus force the fluid through acylinder outlet (not shown) for storage and/or fluid analysis.

Inclusion of the optional dashpot 98 with its compressible fluid thereinprovides a resistive force to the movement of the anchor rod 92 forpressure compensation with regard to the piston 80. The resistive forceproduced within the compressible fluid can be useful in situations whenthe applied force of the pinch brakes (100, 102) is limited and may notpossess sufficient clamping force to support the piston rod 86 againstthe fluid force imparted onto the piston 80. Yet further optionally, thefree end of the anchor rod 92 may include a piston (not shown) forincreasing the resistive force provided by the dashpot 98. Additionally,the resistive force is stored within the compressive fluid and can betransferred into a translational force for pushing the piston 80 backinto the cylinder 82 after the fluid sampling stroke is completed.Alternatives to the fluid can include a spring or other elastic deviceor material in which kinetic energy can be converted to potential energyand temporarily stored therein.

The present invention described herein, therefore, is well adapted tocarry out the objects and attain the ends and advantages mentioned, aswell as others inherent therein. While a presently preferred embodimentof the invention has been given for purposes of disclosure, numerouschanges exist in the details of procedures for accomplishing the desiredresults. For example, the electrically responsive material can be usedfor pressurizing hydraulics, where the produced hydraulic pressure isutilized to operate a drawdown pump as disclosed herein. Moreover, theembodiments of the pumping devices disclosed herein can be utilized formeasuring fluid physical properties such for example fluid density andfluid viscosity. Poiseuille's Law may be implemented with regard tomeasuring fluid viscosity, fluid viscosity can be determined by flowinga known amount of fluid through a length of tube and measuring thepressure drop along the tube. Other ways of determining viscosityinclude rotating a cylinder within the fluid and measuring acorresponding torque produced within the fluid. Rotation of the cylindercan be effectuated by adding a rotary piezo-electric motor. These andother similar modifications will readily suggest themselves to thoseskilled in the art, and are intended to be encompassed within the spiritof the present invention disclosed herein and the scope of the appendedclaims.

1. A formation fluid testing drawdown pump comprising: a piston; acylinder formed to receive said piston therein; and a motive deviceoperatively coupled to said piston, wherein said motive device iscomprised of material responsive to electrical stimuli.
 2. The formationtesting drawdown pump of claim 1, wherein said material is comprised ofa piezoelectric composition.
 3. The formation testing drawdown pump ofclaim 2, further comprising a piezoelectric motor.
 4. The formationtesting drawdown pump of claim 3, wherein said piezoelectric motor isselected from the group comprising a linear piezoelectric motor and arotary piezoelectric motor.
 5. The formation testing drawdown pump ofclaim 1, wherein said material is comprised of an electroactive polymer.6. The formation testing drawdown pump of claim 1, wherein saidoperative coupling is comprised of a direct mechanical attachmentbetween said motive device and said piston.
 7. The formation testingdrawdown pump of claim 1 wherein said operative coupling is comprised ofa hydraulic circuit.
 8. The formation testing drawdown pump of claim 3,wherein said piezoelectric composition comprises at least two distinctpiezoelectric segments.
 9. The formation testing drawdown pump of claim1 further comprising a feed back loop and a pump control, said feed backloop comprising a pressure monitoring device in operative cooperationwith the pump control.
 10. The formation testing drawdown pump of claim9 wherein said pressure monitoring device provides data representativeof fluid pressure within the cylinder and wherein the pump control isprogrammable for controlling the operation of said drawdown pump inresponse to the data representative of fluid pressure within thecylinder to ensure the fluid pressure within the cylinder remains aboveits bubble-point pressure.
 11. A method of sampling connate fluid fromwithin a subterranean formation comprising: inserting a drawdown pumpwithin a wellbore adjacent the subterranean formation; providing a fluidcommunicative path between said drawdown pump and the subterraneanformation; and operating said drawdown pump with a motive device,wherein said motive device is operatively coupled to said drawdown pumpand comprises material responsive to electrical stimuli.
 12. The methodof claim 11 further comprising providing electrical energy to saidmotive device.
 13. The method of claim 11, wherein said material iscomprised of a piezoelectric composition.
 14. The method of claim 13,wherein said piezoelectric composition comprises a piezoelectric motor.15. The method of claim 14, wherein said piezoelectric motor is selectedfrom the group comprising a linear piezoelectric motor and a rotarypiezoelectric motor.
 16. The method of claim 11, wherein said materialis comprised of an electroactive polymer.
 17. The method of claim 11,wherein said operative coupling is comprised of a direct mechanicalattachment between said motive device and said piston.
 18. The method ofclaim 11 wherein said operative coupling is comprised of a hydrauliccircuit.
 19. The method of claim 13, wherein said piezoelectriccomposition comprises at least two distinct piezoelectric segments. 20.The method of claim 13 further comprising monitoring the pressure withinthe cylinder.
 21. The method of claim 20 further comprising controllingoperation of the drawdown pump based on the monitored pressure withinthe cylinder thereby ensuring the pressure within the cylinder remainsabove the bubble-point pressure of the sampled fluid.
 22. The method ofclaim 11, wherein the operating mode of said drawdown pump is selectedfrom the group consisting of operating at a constant pressure andoperating at a constant volumetric flow rate.